1. Field of the Invention
This invention relates to a method of manufacturing the substrate of an electrochromic display cell from a transparent and insulating plate.
Due to their low power consumption, such cells are specially suitable for the display of numeric information or other forms of display in self-contained apparatus powered by primary batteries or accumulators of low capacity. Electronic watches are an example of such apparatus.
In these display cells, the optical properties of the electrochromic material deposited on the electrodes are modified by the action of electrical charges which are produced therein by an electric current which circulates between these electrodes and a counter-electrode through an ionic conductor. It is necessary to prevent any contact between the ionic conductor and the conductive electrodes, so as to preclude any electro-chemical reaction which could lead, for instance, to the dissolution of the electrodes and, consequently, to a much shortened duration of the working life of the cell.
2. Description of the Prior Art
The method usually used for the manufacture of these substrates cannot ensure that such a contact between the ionic conductor and the conductive electrodes does not occur. It consists of depositing a dielectric layer at the desired places through a first protective mask, then depositing a layer of electrochromic material through another mask which is complementary to the first one, that is to say permits the deposition of this electrochromic material at the places left free by the deposition of the dielectric material. There is a big risk, with this method, that the zones which are covered by the dielectric material and the zones covered by the electrochromic material are not exactly contiguous and, consequently, that the ionic conductor can come into contact with the electrodes or their connecting tracks.
Swiss Patent No. 564,227 suggests, but for solving another problem, the provision of a marginal overlap between the electrochromic material and the layer made of dielectric material by which it is surrounded. This arrangement obviously also enables any contact between the ionic conductor and the electrodes or the connecting tracks to be prevented. But, in this case, the coloration created in the zone of the electrochromic material in contact with the ionic conductor diffuses under the marginal protecting zone, and hence cannot later be erased, with the consequential drawback of creating a permanent colored edge at the places of the overlap.